Abstract: Atractylodes macrocephala root rot disease poses a significant constraint on the production of A. macrocephala. The primary pathogens responsible for this disease are Fusarium oxysporum and F. solani. In this study, antagonistic strains B205 and B207 were screened out from 228 bacterial strains isolated from soil samples by the plate confrontation method. The two strains exhibited average inhibition rates of 60.0% and 61.2% against F. oxysporum, and 61.4% and 63.5% against F. solani, respectively. Furthermore, pot experiments demonstrated that these strains had substantial control effects on A. macrocephala root rot disease, with preventing rates of 52.6% for B205 and 76.0% for B207. In addition to their biocontrol capabilities, the optimal concentration for B205 and B207 strains to promote the germination of A. macrocephala seeds was determined to be 1× 10⁹ CFU/mL, and the optimal treatment time was 10 minutes. When seeds were treated with the fermentation broth of B207, significant improvements were observed in various germination indicators compared to the control. Specifically, the germination potential, germination percentage, radicle length, germination index and vigor index increased by 64.2%, 35.3%, 37.2%, 59.0% and 119.9%, respectively. Although B205 fermentation broth also led to higher germination indicators than the control, only the vigor index showed a statistically significant increase. Pot experiments further revealed that both B205 and B207 strains could promote the growth of A. macrocephala seedlings. In particular, B207 treatment significantly increased the plant height, fresh weight, leaf number and root vitality of A. macrocephala plants, with an increase rate of 27.2%, 37.9%, 24.0% and 145.9%, respectively. It also showed a significant promoting effect on the number of buds and the aboveground dry weight. In addition, both B205 and B207 strains can produce IAA, and the amount of IAA produced by B205 and B207 in DF+ medium were 29.58 μg·mL^-1 and 25.62 μg·mL^-1, respectively, which were significantly higher than the control of 7.12 μg·mL^-1. Through 16S rDNA and gyrB gene sequence analysis, strains B205 and B207 were identified as Bacillus velezensis. This study indicates the potential of both B. velezensis B205 and B207 in preventing disease and promoting growth of A. macrocephala. Among them, B207 emerges as a particularly promising microbial strain with biocontrol potential in the production of A. macrocephala.

Key words: Atractylodes macrocephala root rot disease, Bacillus velezensis, antifungal activity, control effect, plant growth promotion